Quality plays important role for sale in the market. To attain this, many industrial managements are eager to use optimization methods to develop product quality. In this study, by evaluating the relationships between product defects and the factors affecting them, ways to improve product quality are presented. Hence, in this paper, a Structural Equation Modeling (SEM) approach is developed to identify the critical factors affecting product quality in paints industry. To this aim, 94 different laboratory samples including hydrocarbon solvent-based paints are assessed. Smart PLS software is utilized to construct the optimized model to determine critical factors. Results show that the different defects affecting the quality of paint are interrelated. In other words, the creation of a flaw will cause other flaws. It has been found that paint surface mottling that depends on the amount of usage of the Bentonite gel, pigment quantity, and resin quality used in the paint formulation affect the other defects such as orange peeling and­ Cratering.